Django ImageField url slow when using Amazon s3

In my Django Application currently running on Heroku I noticed that retrieving url's from ImageFields takes forever when hosting on s3.
The application is written using Django Rest Framework. When I try to retrieve a list of objects that have image fields the response is so slow Heroku throws a timeout error. I assume this is because boto has to retrieve a url from s3 for each individual ImageField upon each request.
How can I speed up the process to prevent these timeout errors?